In the related art, for a structural member having excellent corrosion resistance, particularly having excellent corrosion resistance against sulfuric acid, and requiring hot workability, for example, as disclosed in PTL 1, it is known that a Ni-based alloy is used including, as a composition, by mass %, Cr: 16% to 27%, Mo: 16% to 25% (however, Cr+Mo≦44%), Ta: 1.1% to 3.5%, Fe:0.01% to 6%, Mn: 0.0001% to 3%, Si: 0.0001% to 0.3%, C: 0.001% to 0.1%, Mg: 0.0001% to 0.3%, further, as necessary, one or more of (a) at least one of B: 0.001% to 0.01%, Zr: 0.001% to 0.01%, and Ca:0.001% to 0.01%, (b) at least one of Nb: 0.1% to 0.5%, W: 0.1% to 2%, and Cu: 0.1% to 2%, (c) at least one of Ti: 0.05% to 0.8%, and Al: 0.01% to 0.8%, (d) at least one of Co: 0.1% to 5%, and V: 0.1% to 0.5%, and (e) Hf: 0.1% to 2%, and a balance consisting of Ni and unavoidable impurities.
In addition, as a Ni-based alloy having excellent hot workability and corrosion resistance under an environment that includes chlorine ions, for example, as shown in PTL 2, it is known that a Ni-based alloy is used including, as a composition, by mass %, Cr: 15% to 35%, Mo: 6% to 24% (however, Cr+Mo≦43%), Ta: 1.1% to 8%, Mn: 0.0001% to 3%, Si: 0.0001% to 0.3%, C: 0.001% to 0.1%, N: 0.0001% to 0.1%, and a balance consisting of Ni and unavoidable impurities.